linux-kernel - Re: [PATCH] eCryptFS: mutex lock-unlock ordering fix

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Message-ID: <20080520164217.GB6926@cvg>
Date:	Tue, 20 May 2008 20:42:17 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"Michael A. Halcrow" <mhalcrow@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] eCryptFS: mutex lock-unlock ordering fix

[Cyrill Gorcunov - Tue, May 20, 2008 at 08:39:28PM +0400]
| We should lock/unlock mutexes by a proper way which means
| there should not be chains like ABAB but ABBA otherwise the
| race window is opened.
| 
| Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
| CC: Michael A. Halcrow <mhalcrow@...ibm.com>
| ---
| 
|  check_list:
[...]
|  	if (list_empty(&daemon->msg_ctx_out_queue)) {
NIT ---> | +		if (mutex_is_locked(&ecryptfs_daemon_hash_mux))
| +			mutex_unlock(&ecryptfs_daemon_hash_mux);
|  		mutex_unlock(&daemon->mux);
| -		rc = wait_event_interruptible(
| -			daemon->wait, !list_empty(&daemon->msg_ctx_out_queue));
| +		rc = wait_event_interruptible(daemon->wait,
| +			!list_empty(&daemon->msg_ctx_out_queue));
|  		mutex_lock(&daemon->mux);
|  		if (rc < 0) {
|  			rc = 0;
| @@ -357,6 +358,8 @@ out_unlock_msg_ctx:
|  out_unlock_daemon:
|  	daemon->flags &= ~ECRYPTFS_DAEMON_IN_READ;
|  	mutex_unlock(&daemon->mux);
| +	if (mutex_is_locked(&ecryptfs_daemon_hash_mux))
| +		mutex_unlock(&ecryptfs_daemon_hash_mux);
|  	return rc;
|  }
|  

It's a bit wrong (could release mutex being ack'ed by another thread)
will fix - please DROP this patch. Sorry!

		- Cyrill -
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